Critical exponents and irreversibility lines of La_0.9Sr_0.1CoO₃ single crystal

Abstract

We have studied the dynamic and static critical behavior of spin glass transition in insulating La_0.9Sr_0.1CoO₃ single crystal by ac susceptibility and dc magnetization measurements in the vicinity of its freezing temperature (T_f ). The dynamic scaling analysis of the frequency dependence of ac susceptibility data yields the characteristic time constant τ0=1.6(9)×10⁻¹² s, the dynamic critical exponent zν=9.5(2), and a frequency dependence factor K=∆T_f /T_f (∆logf)=0.017, indicating that the sample enters into a canonical spin-glass phase below T_f=34.8(2) K. The scaling analysis of non-linear magnetization in the vicinity of T_f through the static scaling hypothesis yields critical exponents β=0.89(1) and γ=2.9(1), which match well with that observed for well known three-dimensional (3D) Heisenberg spin glasses. From the longitudinal component of zero-field-cooled and field-cooled magnetization measurement we have constructed the H − T phase diagram which represents the field evolution of two characteristic temperatures: the upper one, T_w(H), indicates the onset of spin freezing in a uniform external field H, while the lower one, T_s(H), marks the onset of strong irreversibility of the frozen state. The low field T_s(H) follows the critical line suggested by d’Almeida-Thouless model for canonical spin glass, whereas the T_w(H) exhibits a re-entrant behavior with a maximum in the T_w(H) at a nonzero field above which it follows the Gabay-Toulouse (GT) critical line which is a characteristic of Heisenberg spin glass. The reentrant behavior of the GT line resembles that predicted theoretically for n-component vector spin glasses in the presence of a uniaxial anisotropy field.